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This is the Canadian Zuba Central Air-to-Air heat pump made by Mitsubishi Electric. Its based off the same technology as City Multi, and can heat with COPs over 1.0 at -30C (-22F). The design day for the area of the install is -18C (0F), and the unit is supposed to have a COP over 1.8 at that temp.

This install is a small cottage, the existing heating source was electric baseboard heaters and this was a full retro with full new metal. HL calc came out at 36,000 BTU, and the 3 ton Mitsubishi unit puts out 40,000 BTU in heating. The heat pump should be able to carry 100% load without the electric backup heater ever firing.

All the bends were done with a tubing bender, there are 3 welds on the whole system.

So how cold will this unit actually run down to and still produce heat?

The heat pump should be able to carry 100% load without the electric backup heater ever firing.

Did you calculate the balance point to make that determination?

How do you mean? There is no need for a balance point calculation with a 1.8 heat pump COP vs. the 1.0 COP of electricity. 1.8>1.0.

The heat loss matches the heat output of the unit. On a design day, the heat pump should run all day, and that is ideal. The electric heater is just a 100% capacity redundant heat source. I actually have the Em. Heat locked out through the Honeywell VisionPro thermostat to not fire unless the temperature drops below -15C (5F).